Firefox simply loses connection and needs a restart

I've used Firefox for years and having installed Beta 1 of FF3.1 a while ago, it would work fine for about half an hour, but then pages would stop loading and it was as if Firefox had lost all connection to the internet. I'd then have to restart a couple of times an hour and this has actually driven me to switch to Chrome but I'd love to switch back if somebody can help me with this.

Having totally uninstalled 3.1 Beta 1, I tried the stable version, and subsequently the Beta 2 and Beta 3, each with no extensions just in case this was the issue but no dice.

Help?